This invention relates to an internal combustion diesel engine having a fuel injection system for injecting fuel directly into one or more combustion chambers, each chamber having an air-intake duct designed as a swirl duct.
In internal combustion diesel engines, since fuel is injected into the cylinder separate from the incoming air, a specific air flow configuration of the air in the combustion chamber is needed in order to form a proper mixture. This defined air flow path, in most engine designs, is obtained with an air-intake duct designed as a swirl duct. A swirl is then imparted to the incoming air which depends on the particular design of the duct and by the particular engine speed. Swirling of the intake air is particularly needed at low operating speeds of the engine, with a certain minimum amount of swirl required to assure a complete homogeneous mixture. The structural design of the swirl duct is usually adapted to provide at least this minimum amount of swirling at low engine speed.
As the engine speed increases, however, the swirl duct configuration represents a restriction in the intake flow, resulting in considerable losses in the delivery rate of air to the engine. This can severely limit the engine performance at higher speeds. At the same time, the increase in the swirl imparted by the swirl duct, resultant from a faster flow of incoming air, is not required to optimize the mixture preparation; that is, complete mixture of the fuel and air will occur anyway with a less swirl.